Contemporary Control Systems Compact Managed Switches Software Manual for Web Browser - Manual (Page 76)

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5.2.6 Message Format for SNMP Operations
Five SNMP operations are used in SNMP version 1: get, get-next, set, get-response, trap. The
first four commands are used to send and receive information for managed objects and use the
same message format. Trap uses a different format discussed in Section 5.2.6.2.
5.2.6.1 Format of Command Messages
Each command message contains a header and a protocol data unit (PDU).
5.2.6.1.1 Message Header
The fields in the message header contain:
Version — 0, indicating SNMP version 1
Community string — The community string, which authorizes NMS access to the switch
5.2.6.1.2 Message Protocol Data Unit (PDU)
SNMPv1 PDUs contain a specific command (get, set etc.) and operands that indicate the object
instances involved in the transaction.
The fields in the PDU contain:
PDU type — Indicates the command type: get(0xA0), get-next(0xA1), set(0xA3), get-response(0xA2)
Request ID — A 4-octet integer used to match response to queries
Error Status — A single octet integer containing a value of zero in a request and the following
error status in a response
noError (0): No problem
tooBig (1): The response to your request was too big to fit into one response.
noSuchName (2): An agent was asked to get or set an OID that it can’t find; i.e., the
OID doesn’t exist. It can be used for an unsupported object.
badValue (3): A read-write or write-only object was set to an inconsistent value.
readOnly (4): This error is generally not used.
genErr (5): None of the previous errors
Error Index — A single octet integer that associates an error with a particular object identifier
(OID). Only the response operation sets this field. Other operations set this field to zero.
Variable binding — contains a sequence of OIDs and values
Figure 49 — Format of the Command Message for SNMP Version 1